Re: Are *observed* SR effects real?
- From: PD <TheDraperFamily@xxxxxxxxx>
- Date: Tue, 29 Jul 2008 07:36:11 -0700 (PDT)
On Jul 29, 8:48 am, mluttg...@xxxxxxxxxx wrote:
On Jul 29, 2:46 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:
On Jul 28, 4:18 pm, mluttg...@xxxxxxxxxx wrote:
On Jul 28, 4:05 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:
On Jul 28, 8:40 am, mluttg...@xxxxxxxxxx wrote:
On Jul 28, 3:22 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:
On Jul 28, 5:20 am, mluttg...@xxxxxxxxxx wrote:
On Jul 27, 9:10 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:
On Jul 26, 8:02 am, mluttg...@xxxxxxxxxx wrote:
On Jul 25, 10:38 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:
On Jul 25, 8:00 am, mluttg...@xxxxxxxxxx wrote:
I retain:
- If you stick to just the suppositions and the logic and never check
in
with reality, then of course it's going to seem just as easy to make
the opposite suppositions. But Nature settles the matter
*definitively*, in experiments designed to check which supposition is
actually right -- this one or that one.
- The strength of SR is not based on the plausibility of its
suppositions and the coherence of arguments that follow, but also on
verification with EXPERIMENT.
So, the obvious questions are:
How did Nature 'decided' that the length of the train is 600 m
in Stan's frame, and 800 m in Tom's frame, and not the
opposite?
(Such 'decision' being compatible with other experiments)..
Is it because the train is moving relative to the Earth, and not
the opposite?
Doesn't such experimental verification falsify SR?
Not at all.
SR explicitly says that the laws of nature work out to demand this:
The physical length of an object is always largest in the frame in
which it is at rest.
This is *precisely* the result that Stan and Tom reproduce in their
measurements, and the result that is confirmed in literally scores of
experiments whose methods and results are recorded in the literature.
In the present case, the longest physical length of the train is the
one measured by Tom, in whose frame the train is at rest.
PD- Hide quoted text -
- Show quoted text -
I am wondering at which scores of experiments you
are referring to, see
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments....
"7. Tests of Length Contraction
At this time there are no direct tests of length contraction, as
measuring the length of a moving object to the precision
required has not been feasible. There is, however,
a demonstration that it occurs:"
The *direct* test has not been done, but neither is it required.. We
knew that the proton had constituents long before there was an
experiment that blew a proton apart and we saw the trails of the
constituents. Same for atoms.
There are a number of indirect but compelling experiments that show
that length contraction occurs at the rate predicted by SR, and this
is alluded to in the web FAQ above.
Right, no direct experiment has been made, but some
experimental results are coherent with the existence
of length contraction.
And now we've explored a little where length contraction comes from,
and it is neither the result of a physical interaction that physically
alters the object, nor is it an illusion stemming from optical
propagation delays.
I repeat what I wrote elsewhere.
From what you wrote earlier:
"Length contraction" results from "the procedure that
*defines* what the length of an object is.
The best procedure for *defining* physical length is to
mark the locations of two events against a standard ruler
*simultaneously*. There is no better definition of
physical length between two events that has ever
been found."
This has nothing to do with a "physical cause".
Marcel Luttgens
At this point in a classroom discussion, when we've moved onto time
dilation, somewhere in somebody's head the wheels about length
contraction are still turning, and something falls softly into place,
and I will usually hear a voice interrupting the discussion:
"You mean that's it?"
And then the conversation goes something like this:
"What do you mean, 'that's it?' "
"I mean, there's nothing more to this special relativity stuff than
that?"
"What were you expecting?"
"To be honest, I was expecting some weird interaction between space
and matter that was making matter shrink. I thought that special
relativity was an effect... the result of some new physics process
that no one was talking about. And I was waiting for you to tell me
about this new physics process. But there's no new physics process,
you're telling me?"
"No, nothing beyond what we've already talked about."
"And so length contraction is nothing more than an artifact of its
definition?"
"More or less. The same is true for momentum."
I wasn't expecting a physical shrinking of matter, as
"void" itself can "contract" according to your definition
of "length contraction".
Yes, that's correct. Keep in mind that I wasn't singling you out when
I was relating the conversation. It is just one that frequently
happens.
"But that's DIFFERENT! I mean, we've been using mass times velocity
for momentum. And ANYONE can see that velocity will depend on the
frame of reference, and so momentum will too. I mean, that's obvious.
Momentum is frame dependent because of its definition, and anyone can
see that."
"Yes, exactly."
"And you've just said that the same is true for length, that length is
frame-dependent because of its definition, and nothing more. And
that's IT??"
"Yup. It took us a few more steps to see it, but that's it in a
nutshell."
"Well, forgive me, but what did Einstein get a Nobel prize for? I
mean, where's the new physics in that?? I thought Einstein invented a
way for space to twist matter and squeeze it and slow down process and
stuff."
"As it turns out, he didn't get the Nobel for relativity, but let's
set that aside for a moment and take a step back. Just two days ago,
you were convinced that length was a frame-independent quantity, much
different than momentum, right?"
I said that there is no direct experimental proof of length
contraction.
But plenty of experimental evidence nonetheless, as I mentioned.
"I suppose..."
"And we had to get through several steps to even get to this point. We
had to recognize that the laws of physics should be the same in every
inertial reference frame.
There is a little problem here, as no frame is really
inertial.
We've talked about this. A frame can be *treated* as inertial if the
tidal effects due to curvature are much smaller than the inertial
effects (such as length contraction) being measured.
Newton's 1st law refers to objects that are in equilibrium, and
strictly speaking, it is extremely rare to find objects that are
absolutely in equilibrium. But even though a coffee cup sitting on a
table is not in equilibrium, for many analyses, it is close enough to
being in equilibrium for Newton's 1st law to be useful and relevant.
Notice for instance that when a train has a.
velocity of about 820 km/h, the SR and GR effects
cancel each other, meaning that a clock on the train
will tick at the same rate as a ground clock.
This is one of the reasons why Einstein devised
general relativity.
Marcel Luttgens
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